When two or more droplets coalesce, they can spontaneously jump away from a superhydrophobic surface due to the release of excess surface energy, which promises enhanced system performance by passively shedding water droplets. See Boreyko, J. B. & Chen, C. H. Self-Propelled Dropwise Condensate on Superhydrophobic Surfaces. Phys Rev Lett 103, 184501-184501-184501-184504, (2009), and Miljkovic, N. et al. Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces. Nano Lett 13, 179-187, (2013), each of which is incorporated by reference in its entirety.
When two discrete fluid droplets merge on a flat surface, they combine to form one larger fluid mass in order to minimize surface energy. When this coalescence process occurs on a suitably designed superhydrophobic surface, the coalesced droplets can spontaneously jump (Boreyko, PRL, 2009). In order to form droplets small enough (≈10-100 μm) to enable jumping, many researchers have resorted to droplet formation via vapor condensation. In addition to enabling the study of droplet jumping, vapor condensation on superhydrophobic surfaces has been a significant topic of interest for a variety of industrial applications due to the reduced steady-state droplet distribution, which enhances heat transfer performance by 30% (Miljkovic, Nano Lett, 2013), reduces ice buildup (Boreyko, J. B. & Collier, P. C. Delayed Frost Growth on Jumping-Drop Superhydrophobic Surfaces. Acs Nano, (2013), which is incorporated by reference in its entirety), and allows for self-cleaning (Wisdom, K., Watson, J., Watson, G. & Chen, C.-H. in 65th Annual Meeting of the APS Division of Fluid Dynamics. (ed Bulletin of the American Physical Society) (Bulletin of the American Physical Society), which is incorporated by reference in its entirety.). To date, researchers have focused on creating superhydrophobic surfaces showing rapid droplet removal (Chen, X. et al. Nanograssed Micropyramidal Architectures for Continuous Dropwise Condensation. Adv Funct Mater 21, 4617-4623, (2011), which is incorporated by reference in its entirety) and experimentally analyzing (Enright, R., Miljkovic, N., Al-Obeidi, A., Thompson, C. V. & Wang, E. N. Superhydrophobic Condensation: The Role of Length Scale and Energy Barriers. Langmuir 40, 14424-14432, (2012), which is incorporated by reference in its entirety.) and modeling (Wang, F. C., Yang, F. Q. & Zhao, Y. P. Size effect on the coalescence-induced self-propelled droplet. Appl Phys Lett 98, (2011), which is incorporated by reference in its entirety.) the merging and jumping behavior prior to and immediately after coalescence. However, aspects related to the droplet charging during the formation, growth and jumping of droplets have not been identified.